[Glitch] Change poll option hover/active styling to be less confusing

Port beb80adb to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/styles/polls.scss

@@ -102,8 +102,8 @@
     &:active,
     &:focus,
     &:hover {
+      border-color: lighten($valid-value-color, 15%);
       border-width: 4px;
-      background: none;
     }
 
     &::-moz-focus-inner {